1. Field of the Invention
The present invention generally relates to the field of instrument flying and, more particularly, is concerned with an instrument flight navigational apparatus and method.
2. Definitions of Instrument Flight Terms
The terms listed below are some of the jargon of instrument flying pertinent to understanding the present invention. Their definitions have been composed from definitions and explanations provided by several texts on instrument flying, namely, "Instrument Flying, 2nd Edition" by Richard L. Taylor (Macmillan Publishing Co., Inc., 1978) and "The Art of Instrument Flying, 2nd Edition" by J. R. Williams (TAB Books, 1991), and on flying in general, namely, "The Pilot's Handbook of Aeronautical Knowledge, Revised and Expanded Edition" by Paul E. Illman (TAB Books, 1991).
The provision of these definitions is, of course, not necessary for one of ordinary skill in the art of instrument flying to understand the present invention. Rather, the definitions of these terms are being set forth for the benefit of those not skilled in this art in order to provide sufficient background to facilitate an adequate understanding of the present invention without the need to consult the cited texts.
The pertinent instrument flying terms and their definitions are as follows:
IFR--This is an acronym for Instrument Flight Rules. However, this term is used universally as a label for all instrument flight operations.
Radio station--This is a ground-based facility at a particular geographical position having either a VOR transmitter or a NDB transmitter which broadcasts a particular signal frequency that can be received by either a VOR receiver or a NDB receiver located on the aircraft when tuned by the pilot to the particular signal frequency.
Course--This is a line drawn on a chart between two points which on IFR charts is assigned a direction referenced as a certain number of degrees clockwise from magnetic north.
Track--This is the path which an aircraft makes across the ground.
Radial--This is a course radiating outwardly FROM a VOR ground station which on IFR charts, as stated above, is assigned a direction referenced as a certain number of degrees clockwise from magnetic north. This is the term used by an air traffic controller (ATC) when referencing navigation instructions relating to a VOR.
Heading--This is the direction in which an aircraft is pointed which in the case of IFR operations is referenced as a certain number of degrees clockwise from magnetic north.
Heading indicator--Also known as a directional gyro, this is an instrument on the aircraft which provides the pilot with the heading of the aircraft.
Vector--This is a heading assigned by an air traffic controller (ATC) for an aircraft to assume.
Bearing--In instrument navigation, this is the direction to or from any point referenced as a certain number of degrees clockwise from magnetic north. In the case of IFR operations, the point is typically a radio station. Where the radio station is a NDB, bearing means the direction toward it. All ADF references are in terms of bearings TO the non-directional beacon (NDB) or other type of radio station; all VOR references are in terms of radials (or bearings) FROM the radio station.
Relative bearing--This is the number of degrees the pointer on an ADF dial is displaced clockwise from the nose of the aircraft. Add relative bearing to heading, and the resulting number is the bearing to the station.
Abeam--This is a position directly off either wingtip of an aircraft, a relative bearing of 90.degree. or 270.degree..
VOR--This is an acronym for a Very high frequency Omni-directional Radio range. A VOR receiver located on the aircraft is composed of: (1) an Omni Bearing Selector (OBS) which is set on a particular course selected by the pilot; (2) a Course Deviation Indicator (CDI), a left-right needle, which will indicate by its position relative to a center line whether the aircraft is centered on, to the left or, or to the right of, the radial that the OBS setting represents; and (3) a TO-FROM indicator which provides information about whether the course (OBS setting) will take the aircraft TO or FROM the VOR omni transmitter located at the particular ground station. If the aircraft is flying a heading that agrees with the course that is set into the OBS, then the aircraft will proceed toward the VOR transmitting ground station if the TO-FROM indicator shows a TO indication, or away from the VOR transmitting ground station if it shows a FROM indication.
NDB--This is an acronym for a Non-Directional Beacon, a radio station upon which is based instrument procedures using an ADF. The NDB employs a low-frequency radio transmitter located at a ground station. An antenna connected to the radio transmitter broadcasts a signal in all directions. The signal, not being concentrated in any one direction, is termed as non-directional or omni-directional.
ADF--This is an acronym for an Automatic Direction Finder, which is a radio compass that includes a low-frequency radio receiver in the aircraft tuned by the pilot for receiving a particular signal frequency from the NDB at a ground station. (The ADF is also tunable to commercial AM-radio broadcast stations for direction-finding or entertainment purposes.) The ADF radio compass also includes a dial having an indicator pointer or needle which points to the radio station to provide the pilot with a readout of the relative bearing from the aircraft to the station where the NDB sending the signal is located. The relative bearing is measured from the nose of the aircraft which is at "0" on the ADF dial. Thus, when the radio station is straight ahead, the relative bearing is "0"; when the radio station is off the right wing tip or left wing tip, the relative bearing is 90.degree. or 270.degree. respectively; when the radio station is straight behind the aircraft, the relative bearing is 180.degree..
Holding Pattern--This is an oval-shaped racetrack flight path which begins and ends at some specified holding point or fix designated by the ATC. There are two types of holding patterns, a standard (right turn) holding pattern or a non-standard (left turn) holding pattern. A holding pattern has a non-holding side which is aligned with a first radial on which lies the holding fix and a holding side which is aligned along a second radial spaced to one side of and generally parallel to the non-holding side.
The terminology used to describe the successively connected legs of a standard (or non-standard) holding pattern, beginning at the holding fix and proceeding in the direction of flight about the holding pattern and ending back at the holding fix, is as follows: (1) a semi-circular fix end leg which turns right (or left in a non-standard holding pattern) from the first radial at the location of the holding fix; (2) a linear outbound leg at the holding side of the pattern which connects with the end of the fix end leg at a point abeam the holding fix; (3) a semi-circular outbound end leg which turns right (or left in a non-standard holding pattern) from the end of the outbound leg; and (4) a linear inbound leg at the non-holding side of the pattern which connects with the end of the outbound end leg and extends along the first radial to the holding fix. The speed of the aircraft is restricted to a certain maximum while in the holding pattern. The length of the inbound leg is defined in terms of time with the aircraft traveling at the maximum holding airspeed: below 14,000 feet altitude, the time of the inbound leg should be one minute, while above this altitude the time is one and one-half minutes. The holding pattern is flown several times to adjust the time of the outbound leg, with the timing commenced abeam the fix, in order to establish the proper time of the inbound leg.
Holding pattern entry--There are three different ways to enter a holding pattern: (1) a direct entry; (2) a parallel entry (at the non-holding side); and (3) a teardrop entry. The correct entry to use depends on the angular relationship of the heading of the arriving aircraft to the radial of the holding fix and to a transverse line which intersects the radial through the holding fix at 70.degree. to the inbound leg on the holding side of the pattern and at 110.degree. from the inbound leg on the non-holding side of the pattern. The three entries are defined hereafter with respect to three arcs composing a 360.degree. circle drawn about the holding fix so as to intersect with the transverse line.
The direct entry to the holding pattern is used when the aircraft is approaching the holding pattern from within a first (180.degree.) arc located at the side of the transverse line upstream from the holding fix and extending through 180.degree. from the end of the line at the holding side, across the first radial, to the end of the line at non-holding side of the pattern. The direct entry involves flying the aircraft to the holding fix and then turning outbound right (or left in the case of the non-standard pattern) in a direction the same as the normal flight direction about the holding pattern.
The parallel entry (at the non-holding side) to the holding pattern is used when the aircraft is approaching the holding pattern from within a second (110.degree.) arc located at the side of the transverse line downstream from the holding fix and extending through 110.degree. from the first radial to the end of the line on the holding side of the pattern. The parallel entry involves flying the aircraft directly across the holding fix, then turning the aircraft to fly the first outbound leg along the non-holding side of the holding pattern, then at the outbound end leg turning the aircraft in a direction opposite to the normal flight direction about the holding pattern in order to intercept the normal inbound leg of the pattern and cross the holding fix and thereafter to enter the normal holding pattern direction at the fix end leg thereof.
The teardrop entry to the holding pattern is used when the aircraft is approaching the holding pattern from within a third (70.degree.) arc located at the side of the transverse line downstream from the holding fix and extending through 70.degree. from the first radial to the end of the line on the non-holding side of the pattern. The teardrop entry involves flying the aircraft directly across the holding fix, then turning the aircraft to fly a heading 30.degree. to the outbound leg for one minute on the holding side of the holding pattern, then at the outbound end leg turning the aircraft in a direction the same as the normal flight direction about the holding pattern in order to intercept the normal inbound leg of the pattern and proceed to the holding fix and thereafter to enter the normal holding pattern direction at the fix end leg thereof.
Procedure turn--This is a turn-around of the aircraft in order to head the aircraft back from where it came on a specific course. Three types of procedure turns are: (1) a 60-second procedure turn which requires about three minutes to complete; (2) a 40-second procedure turn; and (3) a 90-270 degree procedure turn which is the fastest one. The paths of these three types of procedure turns have different closed-loop shapes extending from and back to one side of the course.
The 60-second procedure turn starts with a standard rate 45.degree. turn away from the outbound course (heading is given on the navigational chart), followed by flying a timed leg on a new heading for one minute, followed by a standard rate 180.degree. turn away from the timed leg in a direction opposite the first turn, and then flying an untimed leg on another heading for about one-half minute before intercepting the inbound course.
The 40-second procedure turn is used typically to correct for wind drift or to speed up traffic flow. It starts the same as the 60-second turn with a standard rate 45.degree. turn away from the outbound course and timing also starts at the same place. However, the time of flying the timed leg on the new heading depends on the wind correction factor being added or subtracted. The timed flying leg is followed by a standard rate turn usually of more than 180.degree. to intercept the inbound course.
The 90-270 degree procedure turn is used to turn-around in the minimum amount of time and with the minimum amount of outbound displacement. There is no timing involved and the return to the inbound course will be close to where the departure from the outbound course was made. The turn starts with a 90.degree. turn away from the outbound course and ends with a 270.degree. opposite turn back toward the inbound course.